If you only want to commit some of the changes to a file in a Git repository, use

git add --patch your_changed_file

This will interactively ask you which lines to keep:

$ git add --patch .emacs
diff --git a/.emacs b/.emacs
index d903495..5a0eb9e 100644
--- a/.emacs
+++ b/.emacs
@@ -69,9 +69,9 @@
 ;;; Make better buffer names when opening files with the same name
-(when (autoload 'uniquify "uniquify" "uniquify" t)
+(when (require 'uniquify nil 'noerror)
   (setq uniquify-buffer-name-style 'post-forward-angle-brackets)
-  )
Stage this hunk [y,n,q,a,d,/,K,j,J,g,s,e,?]?

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